The present invention relates to seals, and more particularly, to sealing methods and apparatus used to provide an oil-tight and water-tight seal in structures having transparent or nearly transparent window portions attached to a metal cap covering a sealed assembly, such as an axle bearing or the like.
Several years ago, an important breakthrough was made in the field of providing adequate lubrication to certain types of bearing assemblies, with the result that lubrication intervals were greatly extended, and also that the requirement for periodic maintenance was virtually eliminated. According to this concept, a novel so-called unitized seal was placed within a bearing and axle assembly of the type used on large trucks, tractors, semi-trailers, etc. The novel seal, a typical form of which is shown in U.S. Pat. No. 3,086,781, enabled a relatively low viscosity ("light weight") oil, such as a motor oil (SAE No. 30, for example) to be used in lubricating the bearings instead of the grease formerly used. The bearings in question were typically of the tapered roller configuration, and were in fact better lubricated by grades of oils which were then much lighter or less viscous than the greases previously used.
With the use of heavy grease on wheel bearings of this type, it was necessary to remove the bearings periodically and repack them with the grease. Because grease is not nearly as fluid as oil, and in some cases is not really a fluid at all, continued rotation of the bearings serve gradually to squeeze the grease outwardly from the rollers and bearing races, necessitating periodic repacking. Still further, it is not possible to inspect a bearing using grease from a distance to determine whether it should be re-greased, and accordingly it is the practice with this type of bearing to remove it and pack it periodically, whether or not such repacking is actually necessary.
It will be understood that a common type of bearing failure resulting from lack of lubrication causes bearing seizure, which can in turn cause a vehicle road wheel to be locked to the axle. This commonly results in an accident involving the vehicle, and accordingly, periodic greasing of bearings, being dangerous if neglected, was a very important aspect of vehicle fleet maintenance. Needless to say, considerable cost and labor are involved in disassembling and repacking the bearings in large truck and trailer wheels, with this inherently high cost being further magnified as the cost of labor increases.
With the advent of the unitized wheel seal of the type just described, it became possible to lubricate the wheel bearings with a relatively thin oil, thereby providing not only better lubrication, but lubrication which, because of the high fluidity of the oil, is inherently being constantly replenished at the working surfaces of the bearings. Using this development, it is only necessary to insure that an adequate lubrication level is maintained within the axle housing, and this, according to the invention just referred to, was made possible by providing a transparent cap or cover for the heavy steel hub cap affixed to the end of the axle housing and covering the end of the axle, the axle nut, etc. By using seals of the type described and using hub caps with transparent windows, it is only necessary to look through the window periodically to see that adequate lubricant is present. If so, no maintenance is required, and if the lubricant level is low, a removable plug in the window is removed and additional oil is added. When it is desired to change this oil, which is done only at extended intervals, if at all, it is still not necessary to disassemble the wheel and axle assembly.
As may be expected, making a hub cap having a suitably transparent window was a significant industry problem; this was overcome, however, by using extremely tough but transparent material such as polycarbonate plastics ("Lexan") for example. Plastic materials such as this possess the oil resistance as well as the physical strength necessary to avoid breakage during conditions commonly encountered in heavy duty trucking. Patents showing such hub caps include U.S. Pat. Nos. 3,316,022, 3,177,041 and 3,114,579.
However, there still exists a problem of forming a proper secondary seal between the inner margins of the hub cap defining the window opening and the window itself, and these problems were rendered more difficult to overcome as certain industry, government, and other test standards were adopted, which standards call for exposing the cap and window assemblies to extreme variations of temperature. Accordingly, there has been a significant need for improvement in the effectiveness and reliability of this seal. As appears elsewhere herein, this seal occurs at an interface where at there is considerable differential thermal expansion, distortion, and the like. An ideal seal of this type is one which is easy and reliable to make, which is oil-tight, which is permanent, and which permits significant as well as continual radial expansion and contraction.
Accordingly, it is an object of the present invention to provide an improved secondary seal and method for the foregoing use.
Another object is to provide an improved metal-to-plastic seal which permits significant expansion and contraction in use.
Another object is to provide an improved seal for specialty hub caps and an improved method of making such a seal.
Another object is to provide a hub cap seal which will be highly effective without requiring machining or other special formation of the metal components of the hub cap.
Another object is to provide a specialty seal which includes a metal portion, a plastic portion received within a central opening in the metal portion and which includes an annular groove, a rubber seal member receiving within the groove and a flange locked over the inner margin of the metal cap element so as to apply an axial force to the seal member.
The foregoing and other objects and advantages are achieved in practice by providing a rigid hub cap member, a transparent central window received within an aperture in said cap, means defining a seal receiving groove in the cap, an axially compressible seal member within the groove, and a flange forming a part of the window and extending within the aperture, with the flange being constructed and arranged so as to exert an axial compressive load on the seal member, compressing it between a part of said groove and an inner margin of said cap adjacent said aperture.
The manner in which the foregoing and other objects are carried into practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.